bpfilter: Specify the log level for the kmsg message

[ Upstream commit a196fa7 ]

Per the kmsg document [0], if we don't specify the log level with a
prefix "<N>" in the message string, the default log level will be
applied to the message. Since the default level could be warning(4),
this would make the log utility such as journalctl treat the message,
"Started bpfilter", as a warning. To avoid confusion, this commit
adds the prefix "<5>" to make the message always a notice.

  [0] https://www.kernel.org/doc/Documentation/ABI/testing/dev-kmsg

Fixes: 36c4357 ("net: bpfilter: print umh messages to /dev/kmsg")
Reported-by: Martin Loviska <mloviska@suse.com>
Signed-off-by: Gary Lin <glin@suse.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Dmitrii Banshchikov <me@ubique.spb.ru>
Link: https://lore.kernel.org/bpf/20210623040918.8683-1-glin@suse.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/bpfilter/main.c

@@ -57,7 +57,7 @@ int main(void)
 {
 	debug_f = fopen("/dev/kmsg", "w");
 	setvbuf(debug_f, 0, _IOLBF, 0);
-	fprintf(debug_f, "Started bpfilter\n");
+	fprintf(debug_f, "<5>Started bpfilter\n");
 	loop();
 	fclose(debug_f);
 	return 0;